Grid modulation



W, BUSCHBECK GRID MODULATION Filed Jan. 4, 1950 May 17, 1932.

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INVENTOR WERNER BUSCHBECK A BY WW ATTORNEY Patented May 17, 1932 umran srrs PATENT oFncE WERNER BUSGHBECK, 0F BERLIN, GERMANY, A SSIGNOR TO TELEEUNKEN' GESELL- SCI-IAFT FUR DRAHTLQSE TELE'G-RAPI-IIE M. B. H., OF BERLIN, GER/MANY, A GOR- PORATION 0F GERMANY GRID MODULATION Application filed January 4, 1930, Serial No. 418,477, and in Germany January 7, 1929.

This invention is disclosed in this specification and the accompanying drawings in which Figure 1 illustrates the invention applied to a carrier current telephonic system while Figure 2 shows a similar telegraphic system.

The following invention is based on the switching arrangement as shown in Figure 1. 1 represents the radio frequency tube which is to be modulated. Its direct current grid circuit is blocked ofl by the grid-block-condenser 8. Parallel to the latter is the main modulating tube 2, the grid of which has received such a high negative priming potential from the battery 4; by Way of resistance 5 that it is actually blocked inasmuch as the electromotive force of the battery acts upon the grid with its full strength. Parallel to the gridplate circuit of the main modulating tube there is another tube, the auxiliary modulating tube 3, with a negative electromotive force 6 and an audio frequency transformer 7 in its grid circuit. If this tube is blocked there is no current flowing in the resistance 5, the electromotive force 4 acts with undiminished strength on the grid of the maln modulating tube 2 which blocks the passage of the grid direct current of the radio frequency tube 1. If, by reducing the biasing potential of the auxiliary modulating tube 3 the internal resistance of the latter is made to assume a finite value, a voltage division is obtained over resistance 5 and the internal resistance of the tube 3. The negative biasing grid potential of the main modulating tube 2 decreases in value and finally becomes even positive. Thereby the rid direct current of tube 2 is allowed to ow oil by way of tube 3 which consequently operates only in the negative zone and does not pre-load the audio frequency transformer with direct current.

The chief advantage of this circuit are rangement as compared with the ordinary grid direct current modulation lies in the possibility it affords to utilize the main modulating tube 2 also in the positive part of its characteristic. This may eventually result in a considerable reduction of the number of modulating tubes required. An examaccount of the audio-transformer and for various'other reasons, the modulating tube is able to supply only about milliamperes with the biasing grid potential at zero and a plate voltage of 250 volts. To develop'the full radio frequency power it is therefor necessary to have three modulating tubes connected parallel. With two parallel connected radio frequency tubes 1 the number of modulating tubes would rise to SlX. Now, if it were possible to utilize also the positive part of the modulating tubes characteristic a grid potential of +40 volts with a plate voltage of 250 volts would be sufficient to produce a flow of 150 milliamperes in the tube. The total number of modulating tubes is, therefore, reduced from 6 to 2+1=3. The improvement would be still more conspicuous with a larger number of parallel connected modulating tubes.

Another advantage of this circuit arrangement consists in the influence which the proper selections of electromotive force 4 and of resistance 5 has on the curvature ofthetelephony-curve, straightening it in a large part of its run.

This modulating arrangement may also be used for keying purposes (Fig. 2) by replacing the modulating transformer with a high ohmic resistance 7 and by increasing the electromotive force 6 to a blocking value. The keying relay in this case has to key only the weak current flowing through 7 the voltage of battery 6 being rather low; thus sparkless operation is secured.

I claim: 7

1. A modulating system comprising an electron discharge device having an anode a cathode and a grid, means for subjecting said grid to high frequency potentials, a condenser serially connected between said grid I and said cathode, an electron discharge device having an anode a cathode and a grid electrode, means for connecting its cathode to anode impedance in parallel With said condenser, means for negatively polarizing the grid of said last mentioned electron discharge device, and, another electron discharge device having its output electrodes connected across the grid and anode of the device connected across said condenser, said last mentioned electron discharge device having its input electrode subjected to signaling potentials.

2. A system for producing modulated high frequency Waves comprising a source of high frequency currents, an electron discharge device amplifier having an anode a cathode and a grid coupled to said source, a condenser connected between said grid and catlfode of said amplifier, a normally non-conductive electron discharge device having its anode and cathode connected across said condenser, a resistance and a source of potential connected in series between the cathode and grid of said normally blocked device for imparting to the grid of said device the potential to render it normally non-conductive, and, another electron discharge device having its input electrodes coupled to a source of signaling potentials, having its anode and cathode connected across the grid and anode of said normally non-conductive electron discharge device.

WERNER BUSCHBECK. 

